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Problems in flight-critical drivetrains are a significant cause of catastrophic rotorcraft accidents. Drivetrain breakdowns are also a major factor in aircraft availability rates (mission aborts, unscheduled maintenance operations, and fleet groundings, which demand time and resources for the necessary inspections, corrections, replacements, or repairs). Predicting fatigue failures is difficult and is based primarily on statistical techniques. Improving the reliability of these mechanical systems requires that the design methodology be supported by a more deterministic diagnostic capability once the drivetrain system is introduced into service.
Rotorcraft drivetrain diagnostic research at NASA Lewis is focused on evaluating and developing methods for the early detection of incipient failure or abnormal wear of critical drive-train components. Sensors, recording devices, digital signal processing techniques, and software technologies are being explored and developed to record and monitor drivetrain operating conditions using in-house transmission test stands. Experiments in these test stands evaluate vibration, acoustic, structural, lubricant, and durability characteristics of instrumented transmission systems.
The transmission Health and Usage Monitoring (HUMS) Research Team recently conducted a survey to determine the critical needs of the diagnostics community. The survey results indicated that experimental verification of gear and bearing fault detection methods, improved fault detection in planetary systems, and damage magnitude assessment and prognostics research were critical.
The Lewis research program has recently emphasized investigating the accuracy of a variety of fault detection methods when applied to experimentally obtained HUMS data. Results show that thus far no one fault detection method is successful in predicting all possible failure modes. There is a need to integrate the more successful techniques into one detection parameter. One recently modified method, NA4*, was not only one of the more successful gear fault detectors, it also tracked on damage magnitude to some extent.
Ultimately, the technology evolving from this research will find application in on-board monitoring systems for data collection and processing relating to drivetrain faults and fatigue life consumption. Preventive, on-condition maintenance triggered by the diagnostic system allows for the timely replacement of components prior to failure, extends the productive life of expensive or critical components, and minimizes downtime by ensuring parts are replaced only when wear is evident.
POC: George Bobula
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Updated: March 12, 2004